This paper presents investigations on geochemical species of phosphorus in sediments and vertical distributions of PO₄^3--Pin interstitial waters of Fubao Bay in Lake Dianchi. The sediments of Fubao Bay had high TP contents, with the maximum value of(5630.59±424.25)mg/kg. I-P(inorganic phosphorus) was the major part of TP, which was about 55%-74% of TP. Fe/Al-P (P bound to Al, Fe and Mn oxides and hydroxides) was the major part of I-P, which was about 90% of I-P. The contents of L-P(labile phosphorus)were very low, which was about 0.5％of TP. The Fe/Al-P contents in sediments were very high, which were highly correlated withhigh eutrophication phenomenon and algae blooming events in Fubao Bay, implying a strong diffusion trend for sediment phosphorusin Fubao Bay. Vertical distributions of sediment phosphorus species were complicated, exhibiting a little disorder in both increasedand decreased trends with the depth. This feature was related to the ecosystem conditions, pollutant discharge and sediment dynamicconditions in Fubao Bay. Peeper technique (in situ dialysis membrane samplers) was used to sample interstitial waters in sediments, andvertical distributions of PO₄^3--P were achieved in the waters. The results showed that concentrations of PO₄^3--P in interstitial waters hadgeneral increases followed by decreases with the depth, reflecting a possible diffusion trend for PO₄^3--P from interstitial waters to overlyingwaters. Regression analyses showed that concentrations of PO₄^3--P in the interstitial waters were positively correlated with L-P contents